1. Field of the Invention
The present invention relates to an image taking apparatus and an image taking method for improving an image quality of a taken image by correcting image blur caused by hand shake.
2. Related Background Art
In a recent camera, most of operations important for taking an image such as determination of exposure, and focusing are automated, so even an unskilled operator is not likely to fail in image taking.
Further, in resent times, a system for suppressing hand shake applied to the camera (vibration-proofing system=image stabilizer) has been studied. Therefore, there is almost no cause for failure in image taking.
For the image stabilizer, a system called an optical image stabilizer that detects vibration of the camera due to hand shake and displaces a correction lens in a plane orthogonal to an optical axis in accordance with a result of the determination is widely used.
In order to implement a high performance image stabilizer, it is important, firstly, to precisely detect the vibration of the camera, and secondly, to correct variance in the optical axis caused due to hand shake.
Then, high quality image blurring correction is carried out by driving shake correcting optical means that decenters an image taking optical axis on the basis of an output of a vibration detection section.
The camera shake at the time of taking an image is, in an ordinary case, a vibration of a frequency of 1 to 10 Hz.
Meanwhile, Japanese Patent Application Laid-open No. H05-7336 discloses a method in which an exposure time required for image taking is divided into multiple time periods, a plurality of times of image taking is repeated in a short exposure time to the extent that no hand shake occurs, positional deviations between a plurality of the obtained images are corrected, and thus a combined taken image of a part in which the position of the images are matched is obtained.
In recent times, a digital camera has been more and more miniaturized. The size of the digital camera is made small so as to be embedded in portable electronic apparatuses such as a cellular phone.
In installing a camera that has the optical image stabilizer mentioned above to a small apparatus like this, it is necessary to further downsize the shake correcting optical means, or otherwise, to downsize the vibration detection section.
However, there is a limit for the miniaturization because in the shake correcting optical means, it is necessary to support a correction lens and to drive the correction lens with high accuracy.
In addition, most of the vibration detection sections as presently used utilize inertial force, and therefore there arises a problem in that sensitivity of detection is deteriorated when the vibration detection section is downsized.
Further, as the vibration or shake applied to the camera, there is an angular vibration that is the vibration around a given axis and shift vibration that shakes the camera in parallel directions.
The angular vibration can be corrected by the optical image stabilizer, however, it is difficult to countermeasure the shift vibration.
In particular, as the camera becomes smaller in sizes, the shift vibration tends to be much greater.
On the other hand, as employed in a video camera, there is a method in which a motion vector of the screen is determined by the image taking element, a range of reading the image is varied in accordance with the motion vector, and thereby a motion picture without blur is obtained.
In the case of this method, a dedicated vibration detection section such as the optical image stabilizer as described above and the correction lens are not necessary, and therefore there is such a merit that it is possible to downsize the whole product.
However, it is difficult to apply the image stabilizer of the video camera to the digital camera.
This is because, in the video camera, the motion vector is extracted for each reading of the image and in a case where fifteen frames are extracted per one second, for example, it is necessary to determine the motion vector by comparing the extracted images to one another.
In a case where a still image is taken by the digital camera, only one exposure is carried out in relation to a photographing subject. Accordingly, it is not possible to determine the motion vector by comparing the images as in the case of the video camera.
Therefore, it is difficult to simply adapt the vibration system of the video camera to the digital camera.
On the other hand, in the image stabilization method as disclosed in Japanese Patent Application Laid-open No. H05-7336, the images taken a plurality of times are combined to obtain one image in which image blurring is corrected, and accordingly, the time taken for image taking is long.
In addition, in the present times, most of the cameras are provided with a rapid shooting function for continuously taking a plurality of still images with one single operation of a release switch.
In this regard, if the image stabilization method as disclosed in Japanese Patent Application Laid-open No. H05-7336 is used in combination with the rapid shooting function, there arises a further serious problem in that the time taken for image taking becomes long.